Study of shrinkage–strain and contraction rates of commercial and experimental compomers

Objective To asses the contraction rate and shrinkage–strain of a new experimental compomer in comparison with four commercial compomers and a flowable composite resin. Method Shrinkage–strain and contraction rate were calculated by measuring the deflection of a disc in a developed instrument using “bonded disk” method. Results Both shrinkage–strain and contraction rate are reported. Total shrinkage–strain for compomer systems varies from 2.59 to 3.34%, whereas the flowable composite resin showed a value of 3.50%. The contraction rate for compomers varies from 81.60 to 109.80 μm/min, whereas the flowable composite resin obtained 141.6 μm/min. Commercial compomers show a lower contraction rate than the control group, whereas the experimental group only shows statistical differences with a commercial compomer (Dyract AP). Significance The shrinkage–strain and contraction rate results for the experimental compomer are as good as those obtained for a commercial flowable compomer and a flowable composite resin. The contraction rates of all compomers could be directly related to polymerization rates. The method used to measure shrinkage–strain and contraction rate is adequate because it simulates conditions in situ. It can be inferred that the contraction rate is directly related to shrinkage–strain.